What is a Cell Wall? All living things are composed of cells. They are the building blocks of all life. Cells come in many different shapes and have different functions. Plant and animal cells are different, too. The main difference between plant and animal cells is that plant cells have a cell wall on the outer layer, whereas animal cells only have a cell membrane. The
cell wall is a protective layer outside the cell membrane that also provides support for the cell\’s structure. The cell wall gives the plant its actual shape. It acts as a gatekeeper, because it determines what can come in and out of the cell in order to keep the cell protected. It is kind of like the outside bricks of a castle, only, as you will learn as you read on, there are holes throughout this castle. Those holes do make the cell vulnerable, but they are important to the function of the cell. A redwood tree and a dandelion both have cell walls on the outside of all of their cells. The cell walls are there to give the plants their shape and support; however, the cell walls act and are constructed a little different to meet the needs of the particular plant.
For instance, a 100-foot redwood tree needs a very strong and rigid plant cell wall so that it can grow to its great height and not fall over in the wind. On the other hand, a little yellow dandelion out in the field needs to have more plasticity so that it can bend, not break, as the wind blows through the field. Have you ever forgotten to water the flowers? They may not be able to talk, but they will let you know when they\’re thirsty, as they begin to droop over. Their shape is still being maintained by the cell wall so that, as soon as you water the plant, it can pick itself back up again. On the other hand, if you water too much, the cell wall also makes sure that the cell does not burst. It protects the cell from over-expansion. The cell wall protects the plant and cells from the many insects and pathogens that could harm the plant, but the cell wall still has its vulnerable areas. There are holes all over the cell wall called plasmodesmata. These are holes that allow for nutrients to enter the cell as well as waste to exit the cell.
These small holes can cause the cell to lose water, and this is when the plant will start to droop. But as soon as the plant can get a drink, it will bounce right back up to its proper shape. What Is a Cell Membrane? All living things are made from cells. Plant cells are somewhat unique because unlike animal cells, plant cells contain both a cell wall and cell membrane. Animal cells only have the cell membrane. The cell membrane is a semi-permeable covering surrounding the outside of the cell. Plant cell membranes are found on the outside of the cell cytoplasm and just inside the cell wall. So, the answer to the question, \’Do plant cells have a cell membrane? \’, is \’Yes! \’ Now, what do plant cell membranes actually do? Well, our initial definition said that cell membranes are semi-permeable, and that they surround the cell. This information hints at two primary functions of plant cell membranes. First, the membrane retains the cell\’s cytoplasm and interior parts, and second, it allows specific substances to pass through it, while prohibiting others from doing so.
The first of these functions is fairly obvious. Just like a water balloon holds water inside, the cell membrane holds all cellular components inside. No big surprise there. The membrane, along with the cell wall beside it, keeps the cell together. So rather than focus on the obvious function, let\’s look at the second job: controlling entry and exit from the cell. By controlling what gets into and out of the cell, the membrane is functioning as a regulatory structure. An example of something the plant cell membrane regulates is the release of enzymes. Enzymes are molecules that speed up chemical reactions. One such enzyme belongs to the pitcher plant. These plants are carnivorous and eat insects. The plant cell membrane inside pitcher plants will release enzymes to aid in digestion. Inversely, plant cell membranes can also prevent material from entering the cell. For example, harmful bacteria cannot simply invade the plant cell\’s interior because the membrane will not allow it to cross.